A tape recorder, such as a video cassette recorder or a video camera, includes a head drum assembly containing a video head which is used to either record or play back the video portion on or off a magnetic tape, a rotary drum, a stationary drum and a pair of transformers.
In FIG. 1, there is shown one of the prior art head drum assemblies, which consists of a rotary drum 10 and a stationary drum 11 which are mounted around an upper and a lower portions of a supporting shaft 12, respectively. As shown, the rotary drum 10 is closely fitted around the supporting shaft 12 rotatably supported by the stationary drum 11 via a pair of ball bearings 13a and 13b installed on a bore 11b of a boss 11a. For the installation of the ball bearings 13a and 13b, a pair of bearing seats 11c and lid are formed on an upper and a lower portions of the bore 11b, respectively, which must be accurately sized after a machining process.
Further, a rotor and a stator transformers 14 and 15 are mounted on the head drum assembly, with a predetermined separation therebetween in order to transmit signals between the rotary and the stationary drums 10 and 11. At least two video heads 16 are attached on the rotary drum 10; and a driving motor 17 including a rotor 18 and a stator 19 is positioned under the stationary drum 11.
The head drum assembly constructed in this manner, however, is not easy to assemble, due mainly to the way the ball bearings are installed within the bore of the stationary drum. That is, it is somewhat difficult to precisely align the axis of such bearings with each other or with other parts of the assembly by using a conventional method in which a mandrel or a sizing bar is employed, when the bearings are installed within the head drum assembly.